The present invention relates to a method of producing a pump body and, in particular, to a method of producing a pump body for a micromembrane pump comprising a pump membrane, a pump body and inlet and outlet openings provided with passive non-return valves.
According to the prior art a large number of different micromembrane pumps exists, the drive concepts used being predominantly electromagnetic, thermal and piezoelectric driving principles. Electromagnetic driving principles for micromembrane pumps provided with non-return valves are described e.g. in E. Quandt, K. Seemann, Magnetostrictive Thin Film Microflow Devices, Micro System Technologies 96, pp. 451-456, VDE-Verlag GmbH, 1996.
Thermal drive concepts are explained e.g. in B. Bxc3xcstgens et al, Micromembrane Pump Manufactured by Molding, Proc. Actuator 94; Bremen 1994, pp. 86-90. EP-A-0134614 and H. T. G. Van Lintel et al, A Piezoelectric Micropump Based on Micrmachining of Silicon, Sensors and Actuators, 15, 1988, pp. 153-167, explain piezoelectric driving principles for micromembrane pumps which make use of active or passive non-return valves.
A known micromembrane pump which has an electrostatic drive and which is provided with a pump body having integrated therein an inlet and an outlet opening, which are each provided with non-return valves, is described in R. Zengerle: Mikromembranpumpen als Komponenten fxc3xcr Mikro-Fluidsysteme; Verlag Shaker; Aachen 1994; ISBN 3-8265-0216-7, as well as in DE 41 43 343 A1. Such a micropump is shown in FIG. 1.
The micropump shown in FIG. 1 consists of four silicon chips, two of said chips defining the electrostatic actor consisting of a flexible pump membrane 10 and a counterelectrode 12 which is provided with an insulating layer 14. The two other silicon chips 16 and 18 define a pump body having flap valves 20 and 22 arranged therein. A pump chamber 24 is formed between the pump body, which is defined by the silicon chips 16 and 18, and the flexible pump membrane 10, which is connected to the pump body along the circumference thereof. A spacer layer 28 is arranged between the suspension devices 26 of the flexible pump membrane 10 and the counterelectrode.
When an electric voltage is applied to the electrostatic actor, the elastic pump membrane 10 is electrostatically attracted to the rigid counterelectrode 12, whereby a negative pressure is generated in the pump chamber 24, said negative pressure having the effect that the pump medium flows in via the inlet flap valve 22, cf. arrow 30. When the voltage has been switched off and the charge has been balanced by short-circuiting the electrodes, the pump membrane will relax and displace the pump medium from the pump chamber via the outlet flap valve 20.
With the exception of the different drive means, also a piezoelectrically driven micropump could have the structural design of the micropump body described in FIG. 1.
DE 694 01 250 C2 describes methods for producing a micropump in the case of which a silicon plate having valve structures formed therein is connected to an end plate.
It is the object of the present invention to provide a simple method of producing a pump body at wafer level, said method permitting in addition the production of a pump body which is suitable for producing a micromembrane pump having a high compression ratio.
This object is achieved by a method according to claim 1.
The present invention provides a method of producing a pump body having an inlet opening provided with an inlet valve and an outlet opening provided with an outlet valve. The first step of said method is the step of structuring a respective first main surface of a first and of a second semiconductor disc for defining a valve flap structure of the inlet valve and a valve seat structure of the outlet valve in the first disc and a valve flap structure of the outlet valve and a valve seat structure of the inlet valve in the second disc. Following this, a valve flap well structure and a valve opening well structure are formed in a predetermined relationship with the valve flap structures and the valve seat structures in a respective second main surface of the first and of the second semiconductor disc. The first main surfaces of said first and second semiconductor discs are connected in such a way that the respective valve flap structure is arranged in a predetermined relationship with a respective valve seat structure. Finally, the respective second main surfaces of said first and of said second semiconductor disc are etched at least in the area of the valve flap well structure and of the valve opening well structure so as to expose the valve flaps and open the valve seats.
The above-described electrostatically driven micromembrane pumps have a plurality of disadvantages when used in the form shown e.g. in FIG. 1.
Due to the small stroke of the micromembrane and the comparatively large pump chamber volume, such a known pump has a very small compression ratio. The term compression ratio stands for the ratio of the displaced pumping volume to the total pump chamber volume. Due to this small compression ratio, it is impossible to convey compressible media, such as gases, since the compressibility of such media normally exceeds the compression ratio of the pump.
Furthermore, the pump chamber of the known pump described has a geometry which is disadvantageous as regards fluid dynamics and which is, moreover, not bubble tolerant. Inclusions of air in a fluid pump medium accumulate in the pump chamber and, due to their comparatively high compressibility, they cause a substantial deterioration of the pumping characteristics. In addition, a self-priming behaviour cannot be achieved due to the poor compression behaviour.
Due to the production process used, the pump membrane of the known micropump is, in addition, in electrical contact with the medium conveyed. Since in an electrostatically driven micropump voltages in the order of 200 V occur at the actor during operation, substantial electric potentials may exist in the pump medium in the case of failure, and, depending on the respective case of use, these electric potentials may cause a malfunction of external components. In addition, known micropumps are mounted by glueing individual chips according to the prior art known at present, this kind of mounting being incapable of satisfying the requirements which have to be fulfilled for an efficient production.
Hence, micromembrane pumps with a reduced pump chamber volume would be advantageous for eliminating the above-mentioned disadvantages. One possibility of reducing the pump chamber volume would be to thin the valve chip which faces the drive means. But especially the thinning of such valve chips entails substantial problems. On the one hand, mechanical thinning, e.g. grinding or polishing, may perhaps cause damage to the flap due to the strong vibrations occurring during such mechanical thinning, i.e. the valve flap may break at its fixing point. A chemical process for thinning the valve chip cannot be used either, since the existing valve flaps must be protected against chemical removal, and this is only possible on the basis of a very high investment in the field of process engineering.
The method according to the present invention permits such thinning of the valve chip without any risk of damage being caused to the delicate valve flaps and without any high investment in the field of process engineering.
In addition, the method according to the present invention permits the pump bodies to be produced at wafer level; due to the stacklike structural design, the pump bodies produced are additionally suitable for a final assembly of a micromembrane pump at wafer level; in comparison with numerous other concepts, this is a concept which is very adavantageous from the point of view of production engineering.
Further developments of the present application are disclosed in the dependent claims.